This is somewhat belated, but thank you so much for the feedback (and the prizes - my GB penguin now has a mate). I know I have a long (very long) way to go to become a good writer, but it's good to hear what I need to work on. Kate has (well, will have, eventually, once I get it in postable form) her own story series - the contest entry tells one of her adventures from Ironhoof's standpoint - and the things you noted are all things I had already planned to address there (which is no excuse for leaving them out in this story, I know). Ironhoof, on the other hand, was a definite oversight - I swear I had more of an explanation for why he was guarding the tree in an earlier draft. So, thanks again for the comments. I will definitely be entering further contests (if time permits, of course).
Though I haven't quit, I'm in "lurk mode" right now and will mainly be logging in if I have a new story to post. If you want to contact me, it's better to use one of the other sites I'm on.